This invention relates generally to the transmission of electrical current and voltage from an electrical generator to an electrical bus transmission system and, more particularly, to a high voltage bushing for use in transmitting the electrical current and voltage in the electric generator.
A high voltage bushing is conventionally used for passing an electrical conductor through a pressure vessel wall of, for example, a large generator, without allowing hydrogen gas inside the pressure vessel to leak out of the vessel. The conductor is electrically insulated from the pressure vessel wall by a porcelain sleeve. An asphalt layer is positioned between the porcelain insulator and conductor to provide heat transfer from the conductor out to the porcelain insulator and then to the surrounding hydrogen and air-cooling mediums. However, current construction of conventional high voltage bushings does not adequately protect against the escape of hydrogen out of the pressure vessel or asphalt out of the bushing and is tedious and costly.
The shortcomings of the prior art may be alleviated by using a high voltage bushing in accordance with one or more principles of the present invention.
In one aspect of the invention, there is provided a high voltage bushing comprising an insulator adapted to fit over a conductor and a mounting flange mounted over the insulator. The insulator includes an outer surface defining a flange seat. The mounting flange includes an axial portion and a radial portion located at one end of the axial portion. The axial portion is positioned on the flange seat of the insulator at an end opposite of the radial portion, while the remaining portion of the axial portion joins the insulator by an adhesive layer. In one embodiment, a gasket may be positioned on the flange seat between the insulator and the mounting flange to aid in sealing against the escape of hydrogen.
In another aspect of the invention there is provided a method of assembling the high voltage bushing. The method comprises providing an insulator including an outer surface and defining a flange seat and a mounting flange including an axial portion and a radial portion located at one end of the axial portion. A gasket is positioned on the flange seat of the insulator and the mounting flange is slid onto the insulator until an end of the axial portion opposite the radial portion is positioned in the flange seat of the insulator over the gasket. An adhesive layer is inserted between the mounting flange and the insulator to connect the mounting flange to the insulator while the gasket is used as a dam to prevent leakage of the adhesive.
Additional advantages are provided through the provision of a high voltage bushing having an insulator made from a composite material and a high temperature asphalt material between the conductor and the insulator. The high voltage bushing and method of constructing the high voltage bushing described and claimed herein assures a more reliable gas tight seal between the insulator over the conductor and the mounting flange installed over the insulator to prevent escape of hydrogen from the generator. The gas tight seal is formed by a gasket positioned between the insulator and the mounting flange.
Another advantage of the present invention is the savings in cost and time in assembling the high voltage bushing in accordance with the principles of the present invention. For example, the mounting flange may contact a flange seat formed in the insulator which provides for quick flange installation, accurate flange alignment and reduced construction time of the bushing.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and considered a part of the claimed invention.